Because sometimes it takes time to be able to face your demons.
Life doesn't stop when bad shit happens. You still have to go to the grocery store and do laundry. You still stub your toe on a curb. People still fart on the subway. Sometimes you can let life happen for awhile, let your body heal and your emotions level and your mind strengthen before diving into the reality of what happened. There's no timeframe for this. Days, weeks, months, years. Depends on the person.
How do you know that? (I'm not being facetious.)
I seem to recall there being reasonably solid[1] evidence that thinking about traumatic experiences can actually worsen anxiety and other PTSD symptoms. (Too lazy to look up references, and I don't have access to any paywalled journals anyway, so...) The evidence seems to point to just leaving things be may be better (well, less bad) than trying to "work through" the issues because it means that you'll be wallowing in the traumatic experience over and over.
[1] By psychology standards.
Mind you they _will_ hurt you over time if you just push them away. You probably should get professional help first before trying to meditate.